Installation Location and System Function
Installation LocationThe DSC unit is located in the engine compa~ment in front of the right-hand suspension strut dome.
Construction
The DSC unit consists of the DSC control unit and the hydraulic unit The hydraulic unit comprises principally the valve block and the pump motor.
The following components are integrated in the valve block:
- 2 pump elements driven by eccentric shafts (front-axle brake circuit and rear-axle brake circuit)
- 2 intake valves, 2 switchover valves and 4 inlet valves and 4 outlet valves (12 solenoid valves)
- Internal brake pressure sensor
- 2 accumulators
The (design-related) separating line between the DSC control unit and the hydraulic unit runs through the solenoid valves. The electrical components of the solenoid valves (valve coils) are assigned to the DSC control unit and are directly connected to the board. The mechanical components of the valve (principally the valve domes with the tappets) are affixed to the hydraulic unit.
The DSC control unit is integrated into the vehicle electrical system via a 38-pin connector.
Pin assignment X1746, black
How it works
Pump motor with self-drawing return pump
The return pump is integrated in the hydraulic unit. The return pump contains two pump elements (driven by eccentric shaft) that supply the front-axle brake circuit and rear-axle brake circuit. The return pump is driven by the pump motor.
when ABS regulation is active, the brake pressure at the wheels is regulated by controlled build-up and
reduction of pressure. When pressure is reduced in the wheel brakes, the brake fluid is fed back towards the tandem-brake master cylinder by the return pump.
When automatic stability control is active, the pressure is also built up by the return pump. The direction of activity is determined by the switchover valves. The return pump draws in fluid from the expansion tank via the tandem-brake master cylinder.
Accumulators
The accumulators (1 for each brake circuit) take up the initial volume of brake fluid as pressure is reduced. This volume has to be taken up when ABS, ASC or DSC regulation is active, until the pump motor has run full.
Inlet and outlet valves
The inlet and outlet valves (1 pair for each wheel brake) modulate the pressure in the wheel brakes
during regulation.
Intake valves (high-pressure switching valves) and switchover valves
The intake valves (closed when no current is applied) and the switchover valves (open when no current is applied) - 1 pair for each brake circuit - regulate the build-up of pressure during active DSC brake intervention.
Internal brake pressure sensor
The brake pressure sensor measures the braking pressure applied by the brake pedal and the brake booster. The brake pressure sensor has a measuring range from 0 to 250 bar. Its zero point is continuously adjusted when the brake light switch is not activated and the ignition is switched ON.